![]() ![]() Worse yet, the microcontroller pin P0 will be seeing more than 5V, which greatly exceeds the usual limitation of the microcontroller supply voltage plus 0.3V. Unless the transistor has exceptionally low gain, it will be turned on even though with P0 high it should be turned off. ![]() Assume that P0 is high, at 5V, and R1 is 1000 ohms. R2 would normally have a value high enough to have little effect and ignoring it makes the calculations that follow simpler. ![]() Suppose the load voltage is +12V and the microcontroller is running at 5 volts. Normally it is best to use the same voltage to drive the load that is used to power the microcontroller. One additional thing you need to be careful with PNP high side switches is the voltage used to drive the load. The calculations for base current and the base resistor are identical to those outlined in Part 7 for NPN transistors except the polarities are reversed. With the PNP transistor you need to bring the port pin low to turn on the transistor. With the NPN transistor you set the port pin to the high state to turn on the transistor. The signal needed to control the PNP transistor is also reversed from NPN transistors. This is all backwards compared to an NPN transistor. Base current flows from the emitter to the base, and collector current flows from the emitter. The arrow in the emitter of a PNP transistor points in the opposite direction than in an NPN transistor. Notice that the emitter is connected to the positive voltage. Figure 8-2 shows a circuit using a PNP transistor as a high side switch. Using PNP transistors is essentially the same as NPN transistors, except the polarities are reversed. The alternative is to use a PNP type transistor. As explained in the previous section, negative feedback will prevent the NPN transistor from being driven into saturation. You can’t just connect an NPN transistor’s collector to Vcc and the emitter to the load which is grounded. Figure 8-1 shows the difference between high and low side switching. Sometimes it is desired to have the load at ground potential, and to switch the power supplied to it. With low side switching the load is at Vcc potential. Since the switching element (the transistor) was at ground, it is called a “low side switch.” The load was connected to the power source, and an NPN transistor acted as a switch to ground. Part 7 covered using transistors to switch loads that require higher currents or voltages than the microcontroller can handle. Now wait about 2 min and you will see the switch call home and reg it self with DNA center.This section covers the use of PNP transistors to perform high side switching with a microcontroller. Now wait about 2 min and you will see the switch call home and reg it self with DNA center. #device username admin password 0 password Since we are not going to use vlan 1 on this network we will set pnp to use vlan 900 give it a default gateway to exit the switchĬonfirm you are able to ping the DNA center IP address Note: I checked and it will not show up under provision > inventory > unclaimedĢ. the Distribution or core will not change but we needed to on-board new Access switch with the least of effort and control which switch will call home and get included into the DNA > provision > plug and play settings. This was a setup where you have a Distribution switch and below are all the Access switches. I was able to make it work with the following. Thank you for the Good information and the links to the good data. ![]()
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